A pneumatic tire is a polymeric composite and is a complex system of interacting components, each with specific properties for maximum effectiveness. One of the more important components of a tire is the tread. Since the tread of a tire comes into contact with the road, it is particularly compounded for good traction, good wear characteristics and low rolling resistance. To achieve this combination of properties, blends of various rubbers and other materials (such as fillers, resins, oils and antioxidants) are conventionally used in compounding the tread rubber. The tread of an automobile passenger tire is generally composed of a blend of styrene-butadiene rubber and cis-1,4-polybutadiene rubber. The tread of automobile passenger tires can also contain a wide variety of other rubbery polymers, such as medium vinyl-1,2-polybutadiene rubber, high vinyl-1,2-polybutadiene rubber, 3,4-polyisoprene rubber, isoprene-butadiene rubber, styrene-isoprene rubber and styrene-isoprene-butadiene rubber. Treads for truck and aircraft tires are normally composed of natural rubber or synthetic polyisoprene rubber in blends with synthetic elastomers, such as styrene-butadiene rubber and polybutadiene rubber. However, tread rubbers used in truck and aircraft tires can also contain a wide variety of other rubbery polymers.
It is also important for many tires to exhibit good tear and puncture resistance. This is, of course, because the tire can come into contact with sharp objects and should be capable of resisting puncture or tear. For instance, farm tractor tires frequently run over sharp corn stalks and rocks with sharp edges and should be highly resistant to being punctured by such objects. Earthmover tires also encounter a wide variety of sharp objects at construction sites and must exhibit a high level of resistance to being punctured or torn. Off-the-road tires for trucks and four-wheel-drive vehicles also need to have treads that are highly resistant to tears and punctures.